Conjugated yarn and fiber reinforced plastic

ABSTRACT

A conjugated yarn is provided which is capable of preventing a high-tenacity fiber used therein from being ruptured during a weaving or knitting process. The conjugated yarn includes: core yarns each having a high-tenacity fiber and a reinforcing fiber positioned parallel with the high-tenacity fiber for reinforcing the high-tenacity fiber; and a tying yarn bundling the core yarns. Also provided is a fiber reinforced plastic of which the strength and safety are improved by the use of the conjugated yarn.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a conjugated yarn for use inweaving or knitting of a reinforcing fiber material to be used to ensurethe strength of a carbon fiber reinforced plastic (hereinafter referredto as “CFRP”) for example, and to a fiber reinforced plastic(hereinafter referred to as “FRP”) employing such a conjugated yarn.

[0003] 2. Description of the Related Art

[0004] Various methods have been employed to manufacture CFRP productssuch as shafts of golf clubs, fishing rods and concrete-reinforcingmembers. Widely known ones of such methods include, for example, amethod (1) comprising the steps of: weaving a fabric with a carbon fiberyarn; allowing the woven fabric to be impregnated with a thermosettingresin to form a prepreg; forming the prepreg into a product shape; andthermosetting the prepreg thus shaped, and a method (2) comprising thesteps of: weaving or knitting a preform with a carbon fiber yarn;allowing the preform to be impregnated with a resin matrix; andthermosetting the matrix impregnating the preform.

[0005] Flexure stress works on such a carbon fiber yarn used in themethod (1) or (2) during the weaving or knitting process. If the carbonfiber yarn is ruptured due to such flexure stress, a resulting productcannot ensure a desired strength.

[0006] It has been a conventional practice to lower the weaving orknitting speed or to coat the carbon fiber yarn with a reinforcing resinin order to prevent rupture of such carbon fiber yarn. However, theprior art still have a problem that a satisfactory rupture-preventiveeffect cannot be provided.

[0007] On the other hand, conventional CFRPs involve a problem in termsof safety because they might take dangerous forms when broken.Specifically, though a golf club shaft or ski pole made of metal forexample is not ruptured but merely bent when damaged in use, a golf clubshaft or ski pole formed of CFRP is ruptured at a damaged portion.Ruptured phases of such broken pieces might hurt the body of the user ora person around the user.

[0008] Accordingly, it is a main object of the present invention toprovide a conjugated yarn which is prevented from being ruptured duringa weaving or knitting process.

[0009] Another object of the present invention is to provide aconjugated yarn with which an FRP having higher strength and safety canbe prepared. Yet another object of the present invention is to providesuch an FRP having higher strength and safety.

SUMMARY OF THE INVENTION

[0010] According to a first aspect of the present invention, there isprovided a conjugated yarn: comprising core yarns each comprising ahigh-tenacity fiber and a reinforcing fiber positioned parallel with thehigh-tenacity fiber for reinforcing the high-tenacity fiber; and a tyingyarn bundling the core yarns.

[0011] Since the high-tenacity fiber (carbon fiber, glass fiber, ceramicfiber or the like) and the reinforcing fiber are bundled with the tyingyarn in the conjugated yarn, the high-tenacity fiber is reinforced bythe reinforcing fiber during a weaving or knitting process. Therefore,the high-tenacity fiber will not be ruptured during such a process. AnFRP employing the conjugated yarn according to the first aspect of theinvention exhibits a higher strength as a whole than a conventional oneand hence is hard to break because the high-tenacity fiber forming areinforcing material is reinforced by the reinforcing fiber. When suchan FRP is broken, the reinforcing fiber and the tying yarn serve to tiea broken portion to the rest. Accordingly, even if the high-tenacityfiber is ruptured in the broken portion, the FRP is not ruptured as awhole.

[0012] According to a second aspect of the present invention, there isprovided a fiber reinforced plastic comprising a cured productcomprising a reinforcing fiber material formed of a conjugated yarn asrecited above, and a resin matrix impregnating the reinforcing fibermaterial.

[0013] These and other objects, features and attendant advantages of thepresent invention will become apparent from the following detaileddescription of the present invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic view illustrating one embodiment of thepresent invention; and

[0015]FIG. 2 is an enlarged sectional view taken on line II-II in FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described in detail withreference to the accompanying drawings.

[0017] A conjugated yarn 10 shown in FIG. 1 as one embodiment of thepresent invention forms a reinforcing material for CFRPs used to formgolf club shafts, fishing rods, ski poles, concrete-reinforcing members,aircraft parts, rocket parts and the like.

[0018] The conjugated yarn 10 includes core yarns 16 each comprising ahigh-tenacity fiber 12 and a reinforcing fiber 14, and a tying yarn 18wound around the core yarns 16.

[0019] The high-tenacity fiber 12 is a strand of carbon monofilaments(i.e., high-tenacity monofilaments, hereinafter the same) 12 a havingsuch characteristics as a low elongation, a high elasticity modulus anda high strength. Specific examples of such high-tenacity fibers 12include Torayca produced by Toray Industries Inc. and GRANOC produced byNippon Graphite Fiber Co., Ltd.

[0020] The diameter of each carbon monofilament 12 a forming thehigh-tenacity fiber 12 is not particularly limited but is desirablywithin a range of from 3 to 15 μm from the viewpoint of resistance toflexural fatigue. If the diameter of each carbon monofilament 12 a isless than 3 μm, it is possible that carbon monofilament 12 a is rupturedduring the carbon fiber conjugated yarn making process. If the diameteris more than 15 μm, carbon monofilament 12 a is easy to break when bent.

[0021] Typical carbon fibers include those of the acrylic type which isobtained through sintering of acrylic fibers and those of thepitch-based type which is obtained through sintering of pitch. Thehigh-tenacity fiber 12 (carbon monofilament 12 a) used in thisembodiment may be of either type. The high-tenacity fiber 12 may takethe form of twisted yarn, untwisted yarn, no twist yarn or the like.From the viewpoint of the balance between formability and strength, theform of untwisted yarn or no twist yarn is desirable.

[0022] The reinforcing fiber 14 serves as a splint for reinforcing thehigh-tenacity fiber 12 and comprises a single or plural reinforcingmonofilaments 14 a to be positioned parallel with the high-tenacityfiber 12. Though there is no particular limitation on the type of afiber forming the reinforcing fiber 14 (reinforcing monofilament 14 a),it is desirable that the reinforcing fiber 14, as a whole, exhibit ahigher resistance to flexural fatigue than the high-tenacity fiber 12.Examples of fibers having such a property include titanium fiber,stainless steel fiber, TECHNORA fiber, vinylon fiber, polyamide fiber,polyester fiber, polyvinyl alcohol fiber, polyacrylonitrile fiber, andpolyurethane fiber. Use of polyester fiber or polyamide fiber isdesirable because they are inexpensive and easy to handle.

[0023] In order for the reinforcing fiber 14 to exhibit the CFRP rupturepreventive effect, it is desirable that the reinforcing fiber 14(reinforcing monofilament 14 a) be made using a fiber such as to impartthe reinforcing fiber 14 with a higher resistance to flexural fatigueand a higher tensile elongation at break than the high-tenacity fiber12. Examples of fibers having such properties include titanium fiber,stainless steel fiber, TECHNORA fiber, vinylon fiber, polyamide fiber,polyester fiber, polyvinyl alcohol fiber, polyacrylonitrile fiber, andpolyurethane fiber.

[0024] The tying yarn 18 serves to bundle the core yarns 16 (eachcomprising carbon monofilament 12 a and reinforcing monofilament 14 a)and comprises a single or plural tying fibers 18 a to be wound aroundthe core yarns 16. Though there is no particular limitation on the typeof a fiber forming the tying yarn 18 (tying fiber 18 a), the tying yarn18 is desirably formed of a fiber having a superior abrasion resistancebecause the tying yarn 18 becomes exposed on the outer surface of thecarbon fiber conjugated yarn 10. In order for the tying yarn 18 toexhibit the CFRP rupture preventive effect, it is desirable that thetying yarn 18 (tying fiber 18 a) be made using a fiber such as to impartthe tying yarn 18 with a higher resistance to flexural fatigue and ahigher tensile elongation at break than the high-tenacity fiber 12.Examples of fibers having such properties include titanium fiber,stainless steel fiber, TECHNORA fiber, vinylon fiber, polyamide fiber,polyester fiber, polyvinyl alcohol fiber, polyacrylonitrile fiber, andpolyurethane fiber.

[0025] In making the conjugated yarn 10, the high-tenacity fibers 12 andthe reinforcing fibers 14 are positioned parallel with each other toform the core yarns 16 first. Subsequently, the tying fiber 18 a iswound around the core yarns 16 to cover the same using an Italian-typetwisting machine or a twisting machine for covering for example.

[0026] To prevent torque from working on the conjugated yarn 10,double-covering of the core yarns 16 with tying fibers 18 a wound aroundthe core yarns 16 clockwise and counterclockwise is desired. However,single-covering is sufficient to bundle the core yarns 16.

[0027] In preparing a CFRP (in the form of a golf club shaft, ski poleor fishing rod) using the conjugated yarn 10 there is employed any oneof methods including a method (1) comprising the steps of: weaving afabric (reinforcing carbon fiber material) with conjugated yarn 10;allowing the woven fabric to be impregnated with a resin matrix to forma prepreg; forming the prepreg into a product shape; and thermosettingthe resin matrix forming the prepreg, a method (2) comprising the stepsof: weaving or knitting a preform (reinforcing carbon fiber material)with conjugated yarn 10; allowing the preform to be impregnated with aresin matrix; and thermosetting the matrix impregnating the preform.

[0028] Though flexure stress works on conjugated yarn 10 during theweaving or knitting step of such a method, the high-tenacity fiber 12reinforced by the reinforcing fiber 14 is not ruptured due to suchstress.

[0029] In the CFRP employing the conjugated yarn 10, the high-tenacityfiber 12 forming the reinforcing material is reinforced by thereinforcing fiber 14. Accordingly, if the reinforcing fiber 14 comprisesa fiber having a high resistance to flexural fatigue, the CFRP isimproved in strength as a whole. In the case where the CFRP is appliedto a golf club shaft for example, the resulting golf club shaft is nervyand hence exhibits considerably improved performance.

[0030] When the CFRP employing the conjugated yarn 10 is broken, it ispossible that the high-tenacity fiber 12 is ruptured in the brokenportion. However, the CFRP as a whole can be prevented from beingruptured if the reinforcing fiber 14 and/or the tying fiber 18 are/isformed of a fiber having a high tensile elongation at break.

[0031] That is, if the tensile elongation at break of the reinforcingfiber 14 and/or the tying fiber 18 is higher than that of thehigh-tenacity fiber 12, the high-tenacity fiber 12 is ruptured first,followed by the occurrence of rupture of the reinforcing fiber 14 and/orthe tying fiber 18, provided an equal breaking energy is applied.Actually, however, the breaking energy is attenuated upon rupture of thehigh-tenacity fiber 12 and, hence, the possibility that rupture of thereinforcing fiber 14 and/or the tying fiber 18 is reached is low. Forthis reason the reinforcing fiber 14 and/or the tying fiber 18 play(s)the role of tying the broken portion to the rest, thereby preventing thewhole CFRP from being ruptured in many cases. Accordingly, there is nofear that the ruptured phases of any broken piece hurts a human body.

[0032] The inventor of the present invention conducted the followingtest to verify the effect of the present invention.

[0033] Test Method

[0034] There were provided a high-tenacity fiber consisting of a carbonfiber (67Tex, 100f, 1.6% elongation), a comparative yarn comprising thehigh-tenacity fiber bundled with a vinylon fiber (30 d), and aconjugated yarn comprising the high-tenacity fiber, a stainless steelfiber (40 μm, number of fibers=4) positioned parallel with thehigh-tenacity fiber, and the vinylon fiber (30 d) bundling thehigh-tenacity fiber and the stainless steel fiber. Three types of testsamples (first to third test samples) each comprising 11 test pieceswere woven using the high-tenacity fiber, comparative yarn andconjugated yarn, respectively, as weft and a cotton yarn as warp. Eachof the test samples (11 test pieces of the three types) was subjected toa flexural test.

[0035] Each test sample was of plain weave and was sized about 3.5 cm inthe warp direction×about 18 cm in the weft direction, and the number ofweft yarns of each test sample was 50.

[0036] Test Results

[0037] The test results were as shown in Tables 1 and 2. It was foundfrom the graph of Table 1 that: the first test sample employing only thehigh-tenacity fiber (carbon fiber) as weft did not exhibit a sufficientflexural strength; the flexural strength of the second test sampleemploying the comparative yarn was still insufficient; and the thirdtest sample employing the conjugated yarn 10 exhibited a very highflexural strength.

[0038] It can be predicted from the test results that a fabric employingthe high-tenacity fiber (carbon fiber) only might be ruptured during theweaving process or the like, whereas a fabric employing the conjugatedyarn can solve the problem of rupture because the flexural strength ofthis fabric is remarkably enhanced.

TABLE 2 Test Results First test Second test Third test sample samplesample Strength/weight 1 1.3 1.7 ratio Average (gf-cm) 0.326 0.409 0.688Standard error 0.057 0.020 0.044 Median 0.339 0.400 0.749 Mode # N/A #N/A # N/A Standard 0.190 0.068 0.146 deviation Dispersion 0.036 0.0050.021 Kurtosis −1.453 −1.334 −1.071 Degree of 0.048 0.187 −0.567distorsion Range 0.523 0.203 0.439 Minimum 0.081 0.312 0.453 Maximum0.604 0.515 0.892 Total 3.586 4.495 7.568 Number of 11 11 11 samples

[0039] While the tying yarn 18 is wound around the core yarns 16 in theforegoing embodiment, the tying yarn 18 may be braided around the coreyarns 16 using a braider (for example a braider manufactured by KOKUBUTEKKO CO., LTD.).

[0040] The high-tenacity fiber 12 may be any fiber which has a lowresistance to flexural fatigue but exhibits a high tenacity or any fiberwhich will take a dangerous broken form but exhibits a high tenacity,for example, glass fiber or ceramic fiber.

[0041] It is possible that at least one of the high-tenacity fiber 12,reinforcing fiber 14 and tying yarn 18 may comprise at least two typesof fibers.

[0042] The conjugated yarn of the present invention may be used as areinforcing material for fiber reinforced concrete (FRC).

[0043] According to the present invention, it is possible to preventrupture of the high-tenacity fiber during a weaving or knitting process.Thus, weaving or knitting at a higher speed becomes possible, wherebythe productivity of a reinforcing fiber material or an FRP can beimproved remarkably.

[0044] Since the high-tenacity fiber forming such a reinforcing fibermaterial is reinforced by the reinforcing fiber, an FRP employing thereinforcing fiber material has an enhanced strength as a whole.

[0045] When the FRP employing the conjugated yarn of the presentinvention is broken, it is possible that the high-tenacity fiber isruptured in the broken portion. However, the FRP as a whole can beprevented from being ruptured because the reinforcing fiber and/or thetying fiber play(s) the role of tying the broken portion to the rest.Accordingly, there is no fear that the ruptured phases of any brokenpiece hurts a human body and, hence, the FRP offers remarkably improvedsafety.

[0046] While only presently preferred embodiments of the presentinvention have been described in detail, as will be apparent for thoseskilled in the art, certain changes and modifications can be made inembodiments without departing from the spirit and scope of the presentinvention as defined by the following claims.

What is claimed is:
 1. A conjugated yarn comprising: core yarns eachcomprising a high-tenacity fiber and a reinforcing fiber positionedparallel with the high-tenacity fiber for reinforcing the high-tenacityfiber; and a tying yarn bundling the core yarns.
 2. The conjugated yarnaccording to claim 1, wherein the high-tenacity fiber comprises aplurality of high-tenacity monofilaments.
 3. The conjugated yarnaccording to claim 1 or 2, wherein the reinforcing fiber comprises aplurality of reinforcing monofilaments.
 4. The conjugated yarn accordingto any one of claims 1 to 3, wherein the reinforcing fiber has a higherresistance to flexural fatigue than the high-tenacity fiber.
 5. Theconjugated yarn according to any one of claims 1 to 4, wherein thereinforcing fiber has a higher tensile elongation at break than thehigh-tenacity fiber.
 6. The conjugated yarn according to any one ofclaims 1 to 5, wherein the tying yarn has a higher tensile elongation atbreak than the high-tenacity fiber.
 7. The conjugated yarn according toany one of claims 1 to 6, wherein the tying yarn is wound around thecore yarns.
 8. The conjugated yarn according to any one of claims 1 to6, wherein the tying yarn is braided around the core yarns.
 9. Theconjugated yarn according to any one of claims 1 to 8, wherein thehigh-tenacity fiber comprises a carbon fiber.
 10. The conjugated yarnaccording to any one of claims 1 to 9, wherein the high-tenacity fibercomprises a glass fiber.
 11. The conjugated yarn according to any one ofclaims 1 to 10, wherein the high-tenacity fiber comprises a ceramicfiber.
 12. A fiber reinforced plastic comprising a cured productcomprising a reinforcing fiber material formed of a conjugated yarn asrecited in any one of claims 1 to 11, and a resin matrix impregnatingthe reinforcing fiber material.